FIG. 1 is a sectional view of an apparatus for a conventional method of connecting the armature coil of the rotary machine.
The conventional method will be described referring to FIG. 1. In FIG. 1, the reference numeral (1) designates the shaft of a starter motor; (2) designates an armature core fitted to the shaft; (3) designates an armature coil wound in slots (not shown) formed in the armature core; (3a) designates an end portion of the coil; and (4) designates a commutator to which the end portion (3a) is connected. The commutator (4) comprises a bushing (5) fitted around the shaft (1); a plurality of segments (7) arranged in the same direction as the axis of the shaft (1) so as to provide a sliding surface for brushes (not shown); and a molded substrate (6) for molding these members in one piece. Reference numerals (6a) and (6b) designate edges of the molded substrate (6) for assuring a rigid bonding of the segment (7); (8) designates an ultrasonic welding apparatus which comprises an ultrasonic power producer (9); and FIG. 1 as shown a coil (10), magnetostriction element (11), a horn (12) and a tip (13).
The operation of the structure stated above will now be described. The end portion (3a) of the armature coil put on the end of the segment (7) is applied with compressive force in the direction P and vibrating force in the direction Q, as shown in FIG. 1, by ultrasonic vibration produced by the ultrasonic welding apparatus through the tip (13) so that the end portion (3a) of the coil is firmly connected to the segment (7) by the effect of ultrasonic vibration.
In the conventional ultrasonic welding performed as described above, vibration is applied to the segment (7) by a frictional force caused when the ultrasonic vibration is applied to the end portion (3a) of the coil to release the bonding of the segment from the molded substrate, thereby breaking the molded substrate. Accordingly, it is necessary to receive and absorb the excited vibrating force caused by the ultrasonic wave by the bonding strength of the molded substrate (6). This disadvantageously requires an increased width dimension of end portions (6a), (3b) of the molded substrate; an increased molding surface area for enhancing the bonding strength of the molded substrate (6) to the segment (7); and the provision for a groove for retaining the segment against too high a revolutional velocity. Furthermore, a complicated structure and a requirement of increased volume of materials disadvantageously causes higher manufacturing cost of the commutator.